The present invention relates to a scanning exposure apparatus, and, more particularly, to a scanning exposure apparatus which is used in the lithography process for fabricating micro devices, such as a semiconductor device, liquid crystal display device, image pickup device (CCD or the like) and thin-film magnetic head.
One known scanning exposure apparatus of this type comprises a mask stage on which a photomask or reticle (hereinafter called “mask”) having a circuit pattern formed thereon is to be placed, a substrate stage on which a substrate (wafer, glass plate or the like) coated with a photosensitive material is to be placed, a focusing mechanism which detects surface position information of the substrate and adjustment means which adjusts the surface position of the substrate based on the result of detection by the focusing mechanism. This scanning exposure apparatus moves individual shot areas of a wafer into the exposure field of a projection optical system one after another and sequentially exposes the pattern image of a mask on the individual shot areas.
For example, Japanese Unexamined Patent Publication No. 06-283403 discloses a known surface position setting apparatus (focusing mechanism) for use in such a scanning exposure apparatus. The surface position setting apparatus is provided with multi-point measuring means that measures the height of a substrate parallel to the optical axis of the projection optical system at a plurality of measuring points of the substrate in the scanning direction and a direction intersecting the scanning direction. At the time of scanning the substrate, the surface position setting apparatus measures the height at each measuring point with respect to an exposure field which is conjugate with an illumination area of a predetermined shape with respect to the projection optical system when the substrate is scanned. Based on the maximum and minimum values of the results of measuring the individual measuring points, the surface position setting apparatus acquires the average surface of the exposure surface and then acquires a difference between the height of the average surface and the height of the image surface of the projection optical system. Next, the surface position setting apparatus sets the height of the substrate with the substrate stage based on the difference and aligns the exposure surface.
When the exposure line widths of patterns formed on the individual shot areas of the substrate vary, the conventional scanning exposure apparatus cannot quickly find out the cause or reason for the occurrence of the variation and requires a considerable time and a significant amount of labor to analyze and check the cause.